1. Field of the Invention
The present invention relates to a thermal processing unit and a thermal processing method for carrying out a thermal process while supplying a process gas to an object to be processed.
2. Description of the Related Art
There is a process to form a film on an object to be processed by a so-called reduced-pressure CVD (Chemical vapor deposition) method as one of manufacturing processes of a semiconductor device. A vertical thermal processing unit, as shown in FIG. 9, for example, is used as a unit for carrying out such a film-forming process. This vertical thermal processing unit conducts a thermal process to objects to be processed in a batch manner. Specifically, the vertical thermal processing unit is provided with a cylindrical reaction tube 10 consisting of quartz double tubes, an inner tube 11 and an outer tube 12. A wafer-boat 13 holding many semiconductor wafers (to be referred to as a wafer hereinafter) W, which are the objects to be processed, is conveyed from a lower side of the reaction tube 10 into the reaction tube 10. Inside of the reaction tube 10 is evacuated by a not-shown vacuum pump via a discharging tube 14 so as to be a reduced-pressure atmosphere. On the other hand, a process gas is introduced into the reaction tube 10. A not-shown heater surrounds a side circumference of the reaction tube 10. The film-forming process of the wafers W is carried out by heat generated by the heater.
When the film-forming process is a film-forming process of, for example, a silicon nitride film, ammonium (NH3) gas and dichlorosilane (SiH2Cl2) gas, for example, are used as process gases. A gas-supplying system in this case will be briefly described. The ammonium gas is supplied from a gas supplying source 15a through a gas tube 16a and the dichlorosilane gas is supplied from a gas supplying source 15b through a gas tube 16b, into the reaction tube 10 respectively. Incidentally, in order to make a maintenance cycle of the outer tube 12 longer, nitrogen gas as a purge gas is adapted to be supplied from a gas supplying source 15c through a gas tube 16c into a room between the inner tube 11 and the outer tube 12. Vc1 and Vc2 indicate valves and Mc indicates a flow-rate adjusting part. In the gas tube 16a, a valve Va1, a flow-rate adjusting part Ma, and a valve Va2 are provided in this order from an upstream side thereof. In the gas tube 16b, a valve Vb1, a flow-rate adjusting part Mb and a valve Vb2 are provided as well.
By the way, the aforementioned process gases are poisonous. Therefore, when the processed wafers W are taken out from the reaction tube 10 immediately after the completion of the film-forming process, the poisonous process gases, which remain in the reaction tube 10 and the gas tubes 16a, 16b communicated thereto for supplying the process gases, may be flown to the outside. Therefore, the nitrogen gas is flown from the gas supplying source 15c to the gas tubes 16a, 16b as a replacement gas (purge gas) after the completion of the film-forming process, so that the remaining process gases can be replaced with the nitrogen gas.
Specifically, the gas tube 16c branches into four tubes, i.e. bypass ways 17a, 17b, 18a, 18b at an upstream portion with respect to the flow-rate adjusting part Mc. The bypass ways 17a and 18a are connected to an upstream side and a downstream side with respect to the flow-rate adjusting part Ma of the gas tube 16a, and the bypass ways 17b and 18b are connected to an upstream side and a downstream side with respect to the flow-rate adjusting part Mb of the gas tube 16b. A valve Va3 is provided with the bypass way 17a, a valve Vb3 is provided with the bypass way 17b, a flow-rate adjusting part Md and a valve Vd4 are provided with the bypass way 18a in this order from an upstream side thereof, and a flow-rate adjusting part Me and a valve Vb4 are provided with the bypass way 18b in this order from an upstream side thereof, respectively.
As described above, the nitrogen gas supply is conducted by two lines to each of the gas tubes 16a, 16b that are for supplying the process gases. This is because a flow-rate adjusting range of each of the process gases is narrow and a maximum flow rate of each of the flow-rate adjusting parts Ma, Mb is small. In other words, the bypass ways 18a, 18b are provided in order to ensure a flow rate of the nitrogen gas.
The inventor has been studying a method, for example, illustrated in FIG. 10 as a method for removing a process gas. First of all, at a time t1 when a film-forming process is completed, all the gas supplies into the gas tubes 16a and 16b are stopped. Then, the process gas is discharged toward the discharging tube 14 so that the previous process pressure of 13.3 Pa (0.1 Torr) is reduced to 0.133 Pa. However, the rate for the process gas to be discharged gradually becomes slower. Therefore, in order to enhance a probability of collision of nitrogen gas molecules and process gas molecules by raising the pressure in the reaction tube 10 up to the previous process pressure once, the nitrogen gas supply to the gas tubes 16a and 16b are started (a time t2). This leads a dilution ratio of the process gases remaining in the reaction tube 10 to be lowered to 1.0xc3x9710xe2x88x922. Thereafter, the process gases are discharged toward the discharging tube 14 so as to reduce the pressure at a blast (a time t3). Then, when the nitrogen gas supply to the gas tubes 16a and 16b is started again (a time t4), the concentration of the remaining process gases becomes about 1.0xc3x9710xe2x88x924. By repeating such pressure-raising/lowering steps, the dilution ratio of the process gases in the reaction tube 10 is lowered to be not more than a safety standard value of, for example, 1.0xc3x9710xe2x88x9214.
However, such a dilution process takes a long time, for example, about 30 minutes. This is because a power usage system is arranged at a position away from the thermal processing unit and a gas supplying unit is provided therein. In other words, since a crossover from the gas supplying unit to the thermal processing unit is long, it takes a long time to put out the process gases remaining in this part. Thereby, a period from the completion of the film-forming process of the wafers W to conveyance of the wafers W is long, which is one of causes of the low throughput.
This invention is based on the above issues and the object thereof is to provide a technique capable of shortening a required time from conveying-in of an object to be processed to conveying-out thereof in a thermal processing unit and a thermal processing method, in which a process gas is supplied to the object to be processed so as to conduct a thermal process.
The present invention is a thermal processing unit comprising: a reaction container which an object to be processed is conveyed into and from; a process-gas introducing part for introducing a process gas into the reaction container; a replacement-gas introducing part for introducing a replacement gas into the reaction container, the replacement-gas introducing part being independent of the process-gas introducing part; a discharging part for discharging a gas in the reaction container; and a controlling part connected to the process-gas introducing part, the replacement-gas introducing part and the discharging part, the controlling part being adapted to: control the discharging part so as to lower a pressure in the reaction container lower than a pressure at a thermal process, then control the process-gas introducing part and the replacement-gas introducing part so as to stop introducing the process gas and introduce the replacement gas into the reaction container as well as control the discharging part so as to raise the pressure in the reaction container higher than the pressure at the thermal process, and then control the discharging part so as to lower the pressure in the reaction container lower than the pressure at the thermal process.
According to the feature, it is possible to complete a gas replacement process of the reaction container within a short time, so that it is possible to immediately proceed to a conveying-out step of the object to be processed.
Preferably, the process-gas introducing part has a process-gas way for introducing the process gas into the reaction container and a first open-close unit arranged in a vicinity of the reaction container, the first open-close unit opening and closing the process-gas way, and the controlling part is adapted to control the first open-close unit.
In addition, preferably, the discharging part has a discharging way for discharging the gas in the reaction container and a pressure-adjusting unit arranged in the discharging way, the pressure-adjusting unit adjusting to open and close the discharging way so as to adjust the pressure in the reaction container, and the controlling part is adapted to control the pressure-adjusting unit.
In this case, it is preferable that the thermal processing unit further comprises a bypass way connected between an upstream portion with respect to the first open-close unit in the process-gas way and the discharging way, the bypass way bypassing the reaction container, and a second open-close unit that opens and closes the bypass way.
In this case, it is further preferable that an assistant replacement-gas introducing part for introducing the replacement gas into the processing-gas way is provided at an upstream portion with respect to a position connecting to the bypass way in the process-gas way.
Further preferably, the assistant replacement-gas introducing part has an assistant replacement-gas way for introducing the replacement gas into the process-gas way and a third open-close unit that opens and closes the assistant replacement-gas way.
Further preferably, the controlling part is connected to the second open-close unit and the third open-close unit, is adapted to control the first open-close unit and the third open-close unit to stop introducing the process gas and to introduce the replacement gas into the process-gas way so as to generate a pressure-raised state in the process-gas way, and then is adapted to control the second open-close unit so as to discharge the gas in the process-gas way through the bypass way.
According to the features, it is possible to carry out a gas replacement process in the process-gas way, for example while the object to be processed is conveyed into or from the reaction container. Therefore, the throughput is enhanced.
Moreover, the present invention is a thermal processing method for conducting a thermal process to an object to be processed by using a thermal processing unit comprising: a reaction container which an object to be processed is conveyed into and from; a process-gas introducing part for introducing a process gas into the reaction container; a replacement-gas introducing part for introducing a replacement gas into the reaction container, the replacement-gas introducing part being independent of the process-gas introducing part; and a discharging part for discharging a gas in the reaction container; the method comprising: a first pressure-lowering step of controlling the discharging part so as to lower a pressure in the reaction container lower than a pressure at thermal process, the first pressure-lowering step being conducted after completing the thermal process; a pressure-raising step of controlling the process-gas introducing part and the replacement-gas introducing part so as to stop introducing the process gas and introduce the replacement gas into the reaction container as well as controlling the discharging part so as to raise the pressure in the reaction container higher than the pressure at the thermal process, the pressure-raising step being conducted after the first pressure-lowering step; and a second pressure-lowering step of controlling the discharging part so as to lower the pressure in the reaction container lower than the pressure at the thermal process, the second pressure-lowering step being conducted after the pressure-raising step.
Furthermore, the present invention is a thermal processing method for conducting a thermal process to an object to be processed by using a thermal processing unit comprising: a reaction container which an object to be processed is conveyed into and from; a process-gas introducing part for introducing a process gas into the reaction container; a replacement-gas introducing part for introducing a replacement gas into the reaction container, the replacement-gas introducing part being independent of the process-gas introducing part; and a discharging part for discharging a gas in the reaction container; the process-gas introducing part having a process-gas way for introducing the process gas into the reaction container and a first open-close unit arranged in a vicinity of the reaction container, the first open-close unit opening and closing the process-gas way, the controlling part being adapted to control the first open-close unit, the discharging part having a discharging way for discharging the gas in the reaction container and a pressure-adjusting unit arranged in the discharging way, the pressure-adjusting unit adjusting to open and close the discharging way so as to adjust the pressure in the reaction container, the controlling part being adapted to control the pressure-adjusting unit, the thermal processing unit further comprising: a bypass way connected between an upstream portion with respect to the first open-close unit in the process-gas way and the discharging way, the bypass way bypassing the reaction container; and a second open-close unit that opens and closes the bypass way, an assistant replacement-gas introducing part for introducing the replacement gas into the processing-gas way being provided at an upstream portion with respect to a position connecting to the bypass way in the process-gas way, and the assistant replacement-gas introducing part having an assistant replacement-gas way for introducing the replacement gas into the process-gas way and a third open-close unit that opens and closes the assistant replacement-gas way, the method comprising: a pressure-raising step of controlling the first open-close unit and the third open-close unit so as to stop introducing the process gas and introduce the replacement gas into the process-gas way so as to generate a pressure-raised state in the process-gas way, and a step of controlling the second open-close unit to discharge the gas in the process-gas way through the bypass way, the step being conducted after the pressure-raising step.